Lithium-ion batteries are widely used in electric vehicles due to their high energy density, long cycle life, and excellent stability. However, the significant heat generation caused by power fluctuations under dynamic driving conditions poses substantial challenges to the safety and longevity of the battery. These temperature variations, especially during rapid acceleration or deceleration, can accelerate battery degradation and even thermal runaway. Most existing research focuses on the thermal behavior of batteries under fixed ambient temperatures or constant discharge rates, which fail to fully replicate the diverse and fluctuating conditions that batteries experience in real-world dynamic operations. To address this gap, this study investigates the thermal performance of a battery pack under three typical dynamic operating conditions: steady operation, alternating load operation, and progressive acceleration operations. The experimental results show that at an ambient temperature of 35℃, the direct cooling thermal management system meets the temperature control requirements during steady operation and alternating load operation. However, under progressive acceleration operations, the battery pack's maximum surface temperature reaches 49.8℃, accompanied by a significant temperature difference of 16.5℃, both of which pose risks to battery safety and performance. After the installation of fins, the maximum temperature is reduced to 40.9℃, and the temperature difference drops to 5.0℃. The longitudinal temperature difference decreases from 11.2℃ to 4.6℃, and the transverse temperature difference decreases from 5.9℃ to 1.2℃. The addition of fins not only enhances longitudinal heat conduction but also helpes mitigate the transverse temperature imbalance. These findings underscore the importance of optimizing thermal management strategies. This study provides valuable experimental data to guide the development of more effective thermal management systems for lithium-ion batteries in electric vehicles, ultimately contributing to improved battery safety and longevity under real-world driving conditions.